# SPDX-License-Identifier: GPL-2.0-only
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#
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# Timer subsystem related configuration options
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#
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# Options selectable by arch Kconfig
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# Watchdog function for clocksources to detect instabilities
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config CLOCKSOURCE_WATCHDOG
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bool
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# Architecture has extra clocksource data
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config ARCH_CLOCKSOURCE_DATA
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bool
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# Architecture has extra clocksource init called from registration
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config ARCH_CLOCKSOURCE_INIT
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bool
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# Clocksources require validation of the clocksource against the last
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# cycle update - x86/TSC misfeature
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config CLOCKSOURCE_VALIDATE_LAST_CYCLE
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bool
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# Timekeeping vsyscall support
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config GENERIC_TIME_VSYSCALL
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bool
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# Old style timekeeping
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config ARCH_USES_GETTIMEOFFSET
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bool
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# The generic clock events infrastructure
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config GENERIC_CLOCKEVENTS
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bool
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# Architecture can handle broadcast in a driver-agnostic way
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config ARCH_HAS_TICK_BROADCAST
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bool
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# Clockevents broadcasting infrastructure
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config GENERIC_CLOCKEVENTS_BROADCAST
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bool
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depends on GENERIC_CLOCKEVENTS
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# Automatically adjust the min. reprogramming time for
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# clock event device
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config GENERIC_CLOCKEVENTS_MIN_ADJUST
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bool
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# Generic update of CMOS clock
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config GENERIC_CMOS_UPDATE
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bool
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# Select to handle posix CPU timers from task_work
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# and not from the timer interrupt context
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config HAVE_POSIX_CPU_TIMERS_TASK_WORK
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bool
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config POSIX_CPU_TIMERS_TASK_WORK
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bool
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default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
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if GENERIC_CLOCKEVENTS
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menu "Timers subsystem"
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# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
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# only related to the tick functionality. Oneshot clockevent devices
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# are supported independent of this.
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config TICK_ONESHOT
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bool
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config NO_HZ_COMMON
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bool
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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select TICK_ONESHOT
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choice
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prompt "Timer tick handling"
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default NO_HZ_IDLE if NO_HZ
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config HZ_PERIODIC
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bool "Periodic timer ticks (constant rate, no dynticks)"
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help
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This option keeps the tick running periodically at a constant
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rate, even when the CPU doesn't need it.
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config NO_HZ_IDLE
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bool "Idle dynticks system (tickless idle)"
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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select NO_HZ_COMMON
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help
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This option enables a tickless idle system: timer interrupts
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will only trigger on an as-needed basis when the system is idle.
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This is usually interesting for energy saving.
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Most of the time you want to say Y here.
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config NO_HZ_FULL
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bool "Full dynticks system (tickless)"
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# NO_HZ_COMMON dependency
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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# We need at least one periodic CPU for timekeeping
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depends on SMP
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depends on HAVE_CONTEXT_TRACKING
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# VIRT_CPU_ACCOUNTING_GEN dependency
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depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
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select NO_HZ_COMMON
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select RCU_NOCB_CPU
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select VIRT_CPU_ACCOUNTING_GEN
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select IRQ_WORK
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select CPU_ISOLATION
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help
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Adaptively try to shutdown the tick whenever possible, even when
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the CPU is running tasks. Typically this requires running a single
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task on the CPU. Chances for running tickless are maximized when
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the task mostly runs in userspace and has few kernel activity.
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You need to fill up the nohz_full boot parameter with the
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desired range of dynticks CPUs.
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This is implemented at the expense of some overhead in user <-> kernel
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transitions: syscalls, exceptions and interrupts. Even when it's
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dynamically off.
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Say N.
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endchoice
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config CONTEXT_TRACKING
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bool
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config CONTEXT_TRACKING_FORCE
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bool "Force context tracking"
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depends on CONTEXT_TRACKING
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default y if !NO_HZ_FULL
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help
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The major pre-requirement for full dynticks to work is to
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support the context tracking subsystem. But there are also
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other dependencies to provide in order to make the full
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dynticks working.
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This option stands for testing when an arch implements the
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context tracking backend but doesn't yet fullfill all the
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requirements to make the full dynticks feature working.
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Without the full dynticks, there is no way to test the support
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for context tracking and the subsystems that rely on it: RCU
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userspace extended quiescent state and tickless cputime
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accounting. This option copes with the absence of the full
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dynticks subsystem by forcing the context tracking on all
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CPUs in the system.
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Say Y only if you're working on the development of an
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architecture backend for the context tracking.
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Say N otherwise, this option brings an overhead that you
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don't want in production.
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config NO_HZ
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bool "Old Idle dynticks config"
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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help
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This is the old config entry that enables dynticks idle.
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We keep it around for a little while to enforce backward
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compatibility with older config files.
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config HIGH_RES_TIMERS
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bool "High Resolution Timer Support"
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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select TICK_ONESHOT
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help
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This option enables high resolution timer support. If your
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hardware is not capable then this option only increases
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the size of the kernel image.
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endmenu
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endif
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